Heavy-duty luminaires for outdoor service conventionally utilize a housing of die-cast aluminum. The use of plastic material in lighting fixtures has in general been limited to lightweight and light-duty applications utilizing low wattage lamps. This situation is one of long standing and the outdoor lighting industry almost automatically rejects plastic construction in favor of die-cast fabrication.
The plastic material most adaptable to fixture design is glass fiber-filled polyester resin commonly known as fiberglass. A fiberglass luminaire housing as compared to a die-cast housing is economical, and weathering and corrosive atmospheres are less of a problem. However, fiberglass cannot safely be used in electrical applications as a structural material for the support of heavy components, and Underwriter's Laboratories' regulations severely limit the stress to which it may be subjected. The result has been to substantially rule out up to the present, the use of plastics for the housings of luminaires which must contain heavy components such as iron core transformers and reactors.